(1) Field of the Invention
This invention relates generally to a simulated stop bolt, and more particularly to a calibrated stop bolt including a plurality of strain gauges for accurately measuring the dynamic load applied to the calibrated stop bolt during a shock test.
(2) Description of the Prior Art
Most work to date in torpedo tube shock improvement has centered on variations in the bearing plate and stop bolt designs. However, such modifications are often difficult to implement due to the limited information available on the dynamic loads transmitted to the submarine stop bolt. More particularly, current load limits for submarine stop bolts have been determined from static load tests. These values are conservative for high frequency shock events where higher material strengths are often encountered. This results in the difficulty of implementing modifications since the shock energy must be dissipated, and the load transmitted to the submarine stop bolt is limited, based upon values determined by static testing alone.
Shock test fixtures utilized in conjunction with a heavyweight shock machine are the primary method for testing the effectiveness of torpedo bearing plate designs. In conventional shock testing, the torpedo bearing plate is restrained by a dummy or simulated stop bolt which acts as an interface between the torpedo bearing plate and the shock test fixture to prevent relative motion between the torpedo and the fixture. An example of such a conventional system is shown in FIG. 1, which is a cross-sectional side view of a simulated stop bolt 110, torpedo bearing plate 116 and longitudinal test fixture 126. Stop bolt 110 includes two extensions 114a, 114b which fit through two corresponding holes in the longitudinal test fixture 126, thereby restraining the bearing plate 116 on torpedo 119. By restraining movement of the bearing plate, relative motion between the torpedo and the shock test fixture is prevented. However, conventional longitudinal shock test fixtures are unable to measure the dynamic load transmitted to the simulated stop bolt, thus limiting the ability to improve bearing plate designs.
There is therefore needed an improved simulated stop bolt for shock testing which is capable of measuring the dynamic load transmitted to the simulated stop bolt, so that improvements in the design of torpedo bearing plates and submarine stop bolts can be implemented.
This invention provides a calibrated stop bolt for measuring the dynamic load transmitted to the calibrated stop bolt during a shock test. The stop bolt includes an anterior extension and a posterior extension, for restraining a torpedo bearing plate therebetween, and also includes a plurality of strain gauges mounted at the top portion of each extension. In one embodiment, eight strain gauges are utilized, with two strain gauges placed on each side of the two extensions, i.e., in a full bridge arrangement. The full bridge arrangement is the preferred arrangement because it doubles the rated sensitivity of a single strain gauge. The calibrated stop bolt is preferably mounted to a base plate and bolted at each end to a longitudinal test fixture. The calibrated stop bolt can be utilized with a conventional longitudinal shock test fixture, torpedo shape and heavy weight shock machine, as are known to those of skill in the art.
During a shock test, the bearing plate and calibrated stop bolt engage alternately at the interface between the bearing plate and the anterior and posterior stop bolt extensions, respectively. When the bearing plate and stop bolt engage, the strain gauges measure the strain at each location of the gauges. These strains can then be related to the load experienced at the interface of the bearing plate and the anterior stop bolt extension, and the interface of the bearing plate and the posterior stop bolt extension, so as to determine the dynamic load transmitted to the stop bolt during the shock test. The measurements taken during the shock test may be recorded, for example on a digital recording device, an analogue tape, or computer disc, in order to utilize the measurements in other, subsequent analysis.
It is therefore an object of the present invention to provide a calibrated stop bolt having a plurality of strain gauges mounted thereto for measuring the strain experienced by the calibrated stop bolt.
It is another object of the present invention to provide a calibrated stop bolt capable of measuring the dynamic load transmitted to the calibrated stop bolt during a shock test in order to prove that bearing plate modifications are in compliance with submarine interface requirements.